I use an iPhone 4G supplied by my company. I had a 3G, but I requested the 4G upgrade for the camera capabilities. I used to carry a company camera when I went in the field. Now I don’t have to do so – the iPhone 4G camera is better than the old digital camera that I was using.
FWIW, I carry it in a MagPul field case and currently put that in a Nite-Ize belt case. I am looking for a decent replacement for the Nite-Ize case, though. Just because I use the iPhone as a camera doesn’t mean I want the belt case to look like camera case!